JPH08132192A - Nozzle for continuous casting - Google Patents

Abstract

PURPOSE: To improve the reliability of a continuous casting operation by maintaining an air-tightness of a nozzle for continuous casting in using for long time, realizing the stability at high grade of the service life and obtaining the stability of the continuous casting operation for long time and the improvement and the stability of the quality of a cast slab. CONSTITUTION: In the continuous casting of a metal, an oxidation resistant refractory layer 5 composed of ZrO2 -MgO-SiC-C containing low m.p. glass component over the range of 5-120mm downward from the upper end flat surface 3 on a fitting surface 2 except the range of at least 3mm from the inner hole 4 surface of the air-tightness fitting part 5a is arranged and integrally composed with a refractory member positioned at the upper part which does not contact with the molten metal during casting. By this constitution, the safe and stabilized casting is executed by restraining the oxidation deterioration at the fitting surface and the neighborhood thereof at the time of operating the continuous casting and the stability of the cast slab quality and the improvement of the yield are obtd. by restraining the entrapment of the air and the mixture of non-metallic inclusion, and the service life of the long nozzle can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous casting of metal such as steel, a long nozzle used for pouring down molten metal between a ladle and a tundish, and between a tundish and a mold, and immersion. The present invention relates to suppression and reduction of oxidative deterioration due to contact between a fitting surface of a refractory member located at an upper portion of a continuous casting nozzle such as a nozzle during preheating or during casting, and contact with the atmosphere in the vicinity thereof.

[0002]

2. Description of the Related Art Regarding the prior art, when performing continuous casting of steel, it is installed in the molten steel discharge hole at the bottom of the ladle to prevent the molten steel flowing down from the ladle into the tundish from contacting the atmosphere. Refractory for molten steel downflow passage used for the purpose of suppressing the oxidation of molten steel and preventing the splash of molten steel generated at that time, and injecting molten steel from the ladle into the tundish while rectifying the molten steel flow. A long nozzle (hereinafter referred to as a long nozzle) will be described in detail below with reference to FIG.

The function required of a long nozzle in continuous casting of steel becomes a factor that deteriorates or remarkably destabilizes the quality of the slab due to the fact that the molten metal comes into contact with the atmosphere and is oxidized as described above. Prevents air oxidation, prevents turbulent flow of the molten metal that is being poured down, rectifies the slag to intervene near the surface of the tundish, and to prevent impurities such as non-metallic inclusions from being entrained in the molten metal bath. By suppressing,
In addition to reducing the adverse effect on the quality of the slab and preventing the splash of molten metal to ensure the safety and stability of the continuous casting operation, this long nozzle 1 generally has a material composition It is often used that the fitting portion 5a with the refractory member located in the upper portion is made of Al ₂ O ₃ -C. And this long nozzle 1 is about 70 before use.
In order to prevent the progress of material deterioration due to air oxidation on the outer surface of the long nozzle at the time of preheating in the temperature range of 0 ° C to 1200 ° C, or in the higher temperature range of casting, the above preheating is performed. At the time of casting, it is vitrified by receiving the heat at the time of casting, and an antioxidant that acts to prevent contact between the outer surface and air is applied to the fitting surface 2 with the refractory member located above.

As an example of the material, a material in which SiO ₂ --Al ₂ O ₃ is the main aggregate and potassium silicate or the like is used as a binder has been put into practical use. Especially, the long nozzle is particularly useful in the continuous casting these days. There is a tendency for what is possible over a long period of time, and under these conditions, the long nozzle 1 has a contact pressing action due to fitting when used with a collector nozzle or the like which is a refractory member positioned above, Physical action such as molten steel splash during casting and adhesion and drop of metal, and cleaning by operator to remove foreign matter such as sealing material and metal and slag adhered on the same mating surface every time the pot is replaced Due to the work, the above-mentioned antioxidant coating previously applied to the same surface is destroyed, and in direct proportion to the lapse of time thereafter, locally and gradually over a wide area from the damaged portion of this antioxidant coating. The surface of the long nozzle is directly exposed to the atmosphere and the decarburization phenomenon progresses, and as a result, the surface roughness progresses every time the cleaning work of the mating surface is repeated. The mating surface with the refractory member located on the upper part of the steel deteriorates in material quality, resulting in surface roughening, resulting in a disadvantage that brings a great disadvantage to continuous casting. That is, the above-mentioned deterioration of the fitting surface causes surface roughness during the subsequent use of the long nozzle, and the fitting airtightness between the upper surface and the refractory member is gradually deteriorated as the usage frequency increases. As a result, the reliability of the air sealability originally required for long nozzles decreases, causing air to be entrained in the steel during casting, resulting in destabilization or deterioration of the quality of the slab. Deterioration of the material progresses more significantly due to the inclusion, and even if there is no problem in the subsequent use in other parts with respect to the life of the long nozzle itself, the deterioration of the fitting part makes it impossible to use it further. These are the factors that impair the reliability and economy of continuous casting of steel.

[0005]

In the above-described long nozzle for continuous casting of steel, the following problems have become apparent from the prior art, and obstacles in establishing stable continuous casting operation. It was.

That is, when the long nozzle is used for a long time, as described above, at the fitting surface for connection with the refractory member such as the collector nozzle located above the fitting surface and in the vicinity thereof, at the time of preheating or use. As a result of oxidative decarburization due to the fact that the above-mentioned antioxidant coating is destroyed and the long nozzle material itself comes into direct contact with the atmosphere under conditions where various chemical and physical actions in the same area are applied. The aggregate of the Al ₂ O ₃ -C material and the carbon of the binder are decarburized and disappear, and the tissue structure at that part deteriorates, and the mating surface and its vicinity over time. Not only the phenomenon of the surface layer only, but also gradually progressing deeper toward the inside in the thickness direction.

In the above-mentioned oxidative decarburization part, the original physical strength of the long nozzle material is greatly reduced or completely lost due to the deterioration of the material mainly due to the disappearance of carbon of the aggregate and the binder. According to the above-mentioned various bad conditions such as cleaning and maintenance when casting or changing the pot,
Roughness and loss of the mating surface will occur, impairing the most important airtightness and causing air entrapment, becoming an unacceptable defect seriously adversely affecting the operation of continuous casting of steel Will result in.

From the above, when a long nozzle is used for a long time in continuous casting of metal such as steel, oxidative decarburization occurs at a fitting surface with a refractory member located above a collector nozzle or the like. It was difficult to maintain the airtightness at a safe level by preventing surface roughening without causing deterioration of strength, and there was a trend for commercialization of long nozzles that would enable stable continuous casting operations. .

[0009]

SUMMARY OF THE INVENTION From the background described above, the present invention is to solve the above problems and to maintain the airtightness of a long nozzle for a long time in continuous casting of metal such as steel. The purpose of this is to improve the reliability of continuous casting by achieving higher stability of service life, stabilizing the continuous casting operation for a long time, and improving and stabilizing the quality of the slab. The details will be described below with reference to FIG. 2 by taking a long nozzle used for performing continuous casting of steel as an example.

In continuous casting of steel, when the molten steel is poured down from the ladle into the tundish, the molten metal comes into contact with the atmosphere and undergoes air oxidation, which adversely affects the quality of the slab. Of the long nozzle used to stabilize the steel quality, to ensure safe operation, and to prevent the turbulent flow of the down-flowing molten metal by interrupting the flow of water and preventing the splashing of splashes when pouring the molten metal. During preheating, casting, and waiting during replacement of the pot, oxidative decarburization by direct contact with the atmosphere of the mating surface for connection with the refractory member such as the collector nozzle located at the top On the other hand, by applying an arrangement of a material that is difficult to oxidize to the same portion, oxidation and deterioration are prevented from being suppressed and its reliability is improved.

Long nozzles are generally Al ₂ O ₃ -C-S
iO ₂ material system and Al ₂ O ₃ -C based or these are used mainly material composed by adding SiC, the said surface thereof as the mating surfaces in such a material SiO ₂ -
Al ₂ O ₃ is the main aggregate, and it is protected by an antioxidant coating that uses potassium silicate as a binder, but since the coating thickness is as thin as 0.3 mm to 0.5 mm, it can be used for a long time. When used over a long period of time, the antioxidant coating is destroyed due to various adverse conditions such as the above-mentioned use and maintenance of the long nozzle during standby during ladle replacement, etc., and it is directly proportional to the elapsed time from that site. Oxidative deterioration gradually progresses. As described above, these phenomena have a great adverse effect on the subsequent casting operation and the quality of the slab.

According to the present invention, the thickness of the long nozzle 1 is set below the upper end surface 3 including the fitting surface 2 for connecting the upper surface of the long nozzle 1 to the refractory member such as a sledge of the collector and the vicinity thereof. The oxidation-resistant fire-resistant material layer 5 is integrated in a portion within a range of millimeters to 120 millimeters, excluding a range 6 of at least 3 millimeters from the inner surface of the inner hole, and the material composition is 20 to 75% by weight. ZrO ₂ and 15-65 weight percent MgO and 1-20
An oxidation resistant material composed of weight percent SiC, 10 to 30 weight percent C and 0.2 to 5 weight percent low melting glass components such as frits,
A kneaded material in which these aggregates are mixed, an organic binder is added and kneaded to adjust the particle size is combined with a kneaded material which is a material forming a substantial part such as Al ₂ O ₃ -C so as to have the above-mentioned arrangement, and is used for molding. It is an example of a long nozzle in a continuous casting nozzle obtained by filling a mold, press-molding, and then firing.

The long nozzle 1 has a fitting surface 2 excluding at least 3 mm from the inner surface of the inner hole 4 and its vicinity are protected by an oxidation resistant refractory material. Oxidative deterioration in the vicinity is largely suppressed. If the surface of the antioxidant that has been conventionally used is applied together with the application of this oxidation resistant material to the same portion, the effect can be further enhanced, and an advantageous result can be obtained.

The long nozzle of the present invention is constructed as described above, and oxidation is caused by contact between the fitting surface and the outer surface in the vicinity thereof in the atmosphere during continuous casting operation including preheating in the conventional long nozzle. It greatly suppresses decarburization and material deterioration, improves the safety and stability of continuous casting of steel for a long time, and achieves high-level stabilization of slab quality to improve the reliability of continuous casting and reduce costs. It brings useful effects such as reduction.

The fitting surface 2 for connection with a refractory member such as a collector nozzle, which is located above the long nozzle, is disposed in the vicinity of the inner surface 4 excluding at least 3 mm. ZrO containing fused glass component
Oxidation-resistant fire-resistant material layer 5 composed of _2- MgO-SiC-C
The thickness range of 5 mm to 120 mm is set because the duration of oxidation resistance is too short to sustain long-term use when the thickness is 5 mm or less, and the vicinity of the long nozzle neck is greater than 120 mm. It is because there is little need for it. The reason why the range of at least 3 mm from the long nozzle inner hole 4 is the material of the main body is that the material of the main body to be placed for the purpose of imparting molten steel resistance cannot be within 3 mm due to manufacturing technology.

[0016]

The example of the long nozzle of the present invention is constructed as described above, and suppresses oxidative deterioration of the fitting surface and its vicinity during long-time use between the ladle and the tundish in continuous casting of steel. In addition, safe and stable casting, air entrainment in molten steel and mixing of non-metallic inclusions can be suppressed to stabilize the quality of the slab, improve yield, and extend the life of long nozzles. The result is that the reliability of continuous casting is improved by providing extremely useful effects.

[0017]

The effect was confirmed in the example of the long nozzle of the present invention. In the continuous casting of steel, an attempt was made to perform continuous casting of ordinary steel by mounting it between a ladle having a capacity of 150 tons and a tundish, and the following results were obtained.

With 21 tests and casting of molten steel of 150 tons once as one charge, the total service life was 298 charges and the average service life was 14.2 charges / piece. Incidentally, since the average service life of the conventional long nozzle in the same casting machine was 11.6 charges / piece, the long nozzle of the present invention had a service life improving effect of 24.1%.

Further, as an effect on the quality of the cast product, it was confirmed that the airtightness was improved by 55% in the treated N ₂ concentration verified by the result of the 10th charge.

[0020]

[Table 1]

(*) Note 1) Table 1 compares the air sealability between the conventional product and the product of the present invention by expressing the N ₂ concentration taken into the steel in the unit of PPm. 2) The measuring method was to measure the steel sampled from the ladle and the tundish by the thermal conductivity method. 3) indicates the average value of the measured values of 10 charge content of the resulting value from the N ₂ concentration in the tundish molten steel by subtracting the concentration of N ₂ ladle molten steel. 4) The durability of the long nozzle was an average value of 21 n, which resulted in a 2.6 charge improvement over the conventional product.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional explanatory view of a conventional long nozzle.

FIG. 2 is a vertical cross-sectional explanatory view of a long nozzle of the present invention.

[Explanation of symbols]

 1 Long Nozzle 2 Fitting Surface 3 Upper End Surface 4 Inner Hole 5 Acid Resistant Fireproof Material Layer 5a Fitting Part 6 Range

Claims (1)

[Claims] In continuous casting of metal, the upper end flat surface is the fitting surface excluding at least 3 mm from the inner hole surface of the airtight fitting part with the refractory member located at the upper part that does not come into contact with the molten metal during casting. 5 mm to 1 below
A nozzle for continuous casting, characterized in that an oxidation-resistant refractory material layer made of ZrO ₂ -MgO-SiC-C containing a low-melting glass component over a range of 20 mm is arranged and integrated.